Perceptual Scaling of Map Symbols | Making Maps : DIY Cartography
▻https://makingmaps.net/2007/08/28/perceptual-scaling-of-map-symbols
The implication of this perceptual underestimation was that absolute scaling on proportional symbol maps led to inaccurate perception of the values: while the circles were scaled accurately, the perception of the areas, and thus the values the user got from the map, were wrong.
The solution was to devise a method of perceptual (or apparent) scaling of graduated symbols, or appearance compensation in ArcGIS-ese.
Thousands of perceptual tests led Flannery to develop a method for scaling circles that compensated for the underestimation. When you check the Appearance Compensation check box in ArcGIS the method scales up proportional circles, the larger the circle, the more the scaling.